In the patent document 1, it is disclosed that a pH sensor array is provided with plural pH sensors arranged two-dimensionally to measure the pH distribution of a sample and output the two-dimensional image of the pH distribution measured.
In such a pH sensor array, the reference electrode is placed in contact with the sample to make the potential of the sample stable, similarly in a general pH sensor.
When the exact measurement of the pH value is required in the fields of medicine, biochemistry and so forth, a glass electrode is adopted for the reference electrode.